Dissertation
Understanding and evaluating long-term
environmental risks from landfills
Verständnis und Beurteilung langfristiger
Umweltrisiken von Deponien
ausgeführt zum Zwecke der Erlangung des akademischen Grades eines
Doktors der technischen Wissenschaften unter der Leitung von
o. Univ. Prof. Dr. Paul H. Brunner
Institut für Wassergüte, Ressourcenmanagement und Abfallwirtschaft
eingereicht an der Technischen Universität Wien
Fakultät für Bauingenieurwesen
von
Dipl.-Ing. David Laner
Matrikelnummer: 9740268
Left to themselves, things tend to go from bad to worse.
Murphy’s Law
“… we are aware of the fact that landfilling with contemporary wastes is a large scale long-term experiment for which we have poor knowledge. We also know that in the field of production (supply of consumer goods) we would not run chemical and biological processes under such circumstances.”
Acknowledgments
I thank Paul H. Brunner for the possibility of doing my thesis under his supervision, for his constant support during the last years, and for his constructive criticism helping me to improve my work. I am grateful to Morton A. Barlaz, who agreed to be my co-advisor without really knowing me or my work at that time, who hosted me as a visiting researcher at his department, and whose comments were always thoughtful and highly appreciated.
A lot of nice people work and have worked at the Institute of Water Quality, Resources and Waste Management, whom I want to thank for their support, on an institutional as well as on a personal level. I owe a lot to Johann Fellner, who initiated the research project forming the basis for this thesis, who was always available to discuss about my research and inspire new ideas, and who became a friend during these years. Apart from the friends at the Institute, I had the chance to meet many helpful and inspiring persons in the course of the research project “SKUDENA”, at various scientific conferences, during my research stay in the USA, and during international PhD courses (in particular during the Post Graduate School of Industrial Ecology). To get to know these people was very valuable to me and I hope that many of them will pop up once in a while also in the future.
My family is the foundation of who I am. For their unconditional affection and back up throughout all these years of studying I am very thankful.
I am indebted the most to my beloved Monika. She motivated me when work had become tedious, she listened to me even if I was not coming straight to the point, she broadened my perspective on many things, and her smile made everything else secondary. Sharing my life with her is a great fortune.
Abstract
After closure, landfills need to be managed (i.e. monitoring and maintenance) and controlled to avoid adverse effects on humans and the environment. The aftercare period ends when a landfill is no longer likely to represent a threat to human health or the environment. As quantitative criteria to determine the state of a landfill at the end of aftercare have been missing, it was the aim of this work to develop a methodology for evaluating the environmental compatibility of a closed landfill in view of aftercare completion. The methodology takes into account the behavior of the deposited waste and associated emissions, the performance of technical barriers, the potential for the migration of pollutants in the environment, and the impact of landfill-borne pollutants on environmental media.
Landfill behavior and associated emissions were analyzed for different types of landfills. Based on literature data and landfill data collected at sites in Austria and Switzerland, emission characteristics of landfills and their evolution over time, remaining emission potentials, and approaches to predict future landfill emissions were evaluated. Though organic leachate emissions and constituents such as ammonium or chloride are of potential significance at many closed landfills, the type of pollutants and emission levels vary from one site to another. The impact of substances mobilized from the deposited waste on the surrounding environment is potentially mitigated by technical and natural barriers at the landfill. The long-term efficiency of technical barriers (i.e. landfill containment) to limit and control the interaction of the deposited waste with the surrounding environment was evaluated based on literature data and expert surveys using a Delphi approach. Due to the large uncertainties inherent in long-term evaluations, scenarios are used to illustrate the effect of different technical barrier performance levels on emissions. The potential of the natural environment to attenuate adverse effects of released landfill borne pollutants was evaluated by pollutant migration models. In general, simple and robust models were used to describe pollutant migration in the environment, as data to establish and calibrate more complex models are typically not available at closed landfills. Finally, scenario- and pollutant-specific aftercare completion criteria were derived based on the combination of the different models and the definition of an acceptable level of impact on the environment (e.g. groundwater) at the site.
The developed methodology was applied at three closed landfill sites to derive aftercare completion criteria and estimate the duration of aftercare. For a large municipal solid waste (MSW) landfill, the aftercare period is estimated to last from one century to several centuries, depending on the long-term management concept at the site. At a smaller MSW landfill with high water infiltration rates (annual precipitation of 2000 mm/yr), aftercare might be terminated within a few decades, provided that intensified leaching of the waste is continued for another decade before final cover installation. For a closed landfill containing building and construction (C&D) waste, aftercare completion is found to be environmentally tolerable already after a few years, provided that the assumptions and models in the evaluation are confirmed by further monitoring. The main reasons for the low environmental risk associated with the C&D landfill are the small emission potential of the deposited waste, the arid climate (and low amount of leachate), and the large dilution potential of the local groundwater stream. The case study findings highlight the importance of site-specific factors for the evaluation of landfill aftercare and underline the site-specific nature of the evaluation of landfill environmental compatibility. The evaluation methodology allows for a comparison of different long-term management strategies in view of the desired state of the landfill at the end of aftercare. Thus, it links the duration and intensity of landfill management to the environmental risks associated with a closed landfill, which is a prerequisite to developing cost-effective long-term landfill management concepts.
Table of Contents
1 Introduction ... 1
1.1 Background and motivation... 1
1.2 Objectives and scope of the work ... 2
1.3 Structure of the thesis... 2
2 Aftercare completion criteria and landfill stability... 5
2.1 Concepts for aftercare and completion ... 5
2.1.1 General overview ... 5
2.1.2 Review of approaches for landfill aftercare and its completion... 7
2.1.3 Discussion of approaches to evaluate aftercare ... 16
2.2 Landfill stability – definition and metric ... 18
2.2.1 The notion of “landfill stability”... 18
2.2.2 Framework to evaluate landfill PCC... 21
3 Emission behavior of landfills ... 25
3.1 Emissions from MSW landfills... 25
3.1.1 General description of emission behavior... 25
3.1.2 Emission characteristics of MSW landfills... 30
3.1.3 Evaluation of mid- to long-term emissions... 39
3.2 Emissions from landfills containing MSWI bottom ash ... 43
3.2.1 General description of emission behavior... 43
3.2.2 Emission characteristics of MSWI bottom ash landfills ... 46
3.2.3 Evaluation of mid- to long-term emissions... 52
3.3 Emissions from landfills containing construction and demolition wastes ... 54
3.3.1 General description of emission behavior... 54
3.3.2 Emission characteristics of C&D waste landfills... 55
3.3.3 Evaluation of mid- to long-term emissions... 60
3.4 Key parameters to evaluate landfill emission behavior ... 62
4 Barriers – technical and natural systems ... 65
4.1 Technical barriers... 65
4.1.1 Components of technical barriers ... 67
4.1.2 Performance of landfill top cover systems... 73
4.1.3 Performance of technical barriers at the landfill bottom... 76
4.1.4 Long-term performance of technical barriers ... 79
4.1.5 Summary and discussion... 85
4.2 Natural systems attenuating landfill emissions ... 86
4.2.1 Overview... 86
4.2.2 Leachate migration in the subsurface... 88
5 Evaluation method to determine aftercare completion criteria... 103
5.1 Evaluation of the state of the landfill and the site... 104
5.1.1 General data on the conditions at the site ... 104
5.1.2 Emission data ... 105
5.1.3 Deposited waste ... 106
5.1.4 Containment system... 108
5.1.5 Geology and hydrogeology at the site... 109
5.2 Emission models and scenario-based predictions ... 109
5.2.1 Emission models ... 110
5.2.2 Scenario layouts ... 116
5.3 Pollutant migration modeling and ambient concentrations... 126
5.3.1 Pollutant migration model in the subsurface... 126
5.4 Determination of completion criteria... 137
6 Case studies... 139
6.1 Landfill A - closed MSW landfill ... 140
6.1.1 Site description and monitoring data ... 140
6.1.2 Emission predictions... 143
6.1.3 Pollutant migration... 152
6.1.4 Completion criteria and aftercare duration ... 157
6.2 Landfill B - closed MSW landfill ... 159
6.2.1 Site description and monitoring data ... 159
6.2.2 Emission predictions... 162
6.2.3 Pollutant migration... 168
6.2.4 Completion criteria and aftercare duration ... 172
6.3 Landfill C - closed C&D waste landfill ... 174
6.3.1 Site description and monitoring data ... 174
6.3.2 Emission predictions... 177
6.3.3 Pollutant migration... 182
6.3.4 Completion criteria and aftercare duration ... 186
6.4 Discussion of caste study results... 187
7 Summary and conclusions ... 191
7.1 Summary ... 191
7.1.1 Landfill emission behavior... 191
7.1.2 Technical and natural barriers... 193
7.1.3 Methodology to derive aftercare completion criteria... 195
7.1.4 Application of the methodology ... 196
7.2 Conclusions and research outlook... 198
8 Literature, Figures, and Tables... 201
8.1 Literature... 201
8.2 List of Figures ... 217
Appendices 225
Appendix 1: Basic landfill data
List of Acronyms
AF Attenuation factorAOX Absorbable organic halides
BOD5 Biological oxygen demand in 5 days
BTEX Benzene, toluene, ethylbenzene, and xylenes
C&D Construction and demolition
COD Chemical oxygen demand
DM Dry matter
DOC Dissolved organic carbon
EC Electric conductivity
GCL Geosynthetic clay liner
HDPE High density polyethylene
HHE Human health and the environment
L/S Liquid-to-solid ratio
LDPE Low density polyethylene
LSR Landfill simulation reactor
MBT Mechanical biological treatment
MSW Municipal solid waste
MSWI Municipal solid waste incineration
PAH Polycyclic aromatic hydrocarbons
PCC Post-closure care
PVC Polyvinylchloride
QA&C Quality assurance and control
SP Service period
TKN Total Kjeldahl nitrogen
TOC Total organic carbon
Glossary
Aftercare completion: The point in time when the authorities accept the end of aftercare, because the landfill is no longer likely to present a threat to human health and the environment in the absence of aftercare.
C&D waste landfill: A landfill which contains primarily construction and demolition (C&D) waste. Contaminant: A substance, the presence of which is unwanted in a material.
De-minimus care: Low-intensity landfill management comprising levels and types of activities also required at non-landfill sites (e.g. maintenance of a vegetation cover).
Environmental risk: The integration of the probability of occurrence of a release of pollutants from the landfill and the damage caused by the pollutant in the environment.
Field capacity: The volumetric water content of a porous medium 2-3 days after saturation and after gravity drainage has ceased.
Final storage quality: Expresses that a material can be deposited without containment and without treatment of emissions into air and water.
Hydraulic conductivity: A property which describes the ease with which water can move through a porous medium.
Landfill aftercare: The management of a closed landfill (typically monitoring, maintenance, and treatment of emissions) until no more aftercare measures are necessary (landfill aftercare = landfill post-closure care).
Landfill after-use: The use of a landfill site which has been released from aftercare.
Landfill closure: The point where the landfill has reached the layout according to the aftercare requirements (i.e. installation of top cover) and is transferred to the aftercare period.
Landfill operation period: The time period during which waste is deposited at the landfill.
Landfill owner: The individual who has operated the landfill and is responsible for landfill management (landfill owner = landfill operator).
Leachate: A liquid generated in a landfill that contains dissolved and/or suspended contaminants from the waste.
Mobilizable substance potential: The amount of substances which can be released from the waste via a specific emission pathway. The mobilizable substance potential depends on the considered release mechanisms and thus, is a function of the investigation timeframe. MSW landfill: A landfill which contains primarily municipal solid waste (MSW).
MSWI bottom ash landfill: A landfill which contains primarily bottom ash from municipal solid waste incineration (MSWI).
Natural attenuation: The reduction of mass, toxicity, mobility, volume, or concentration of pollu tants in soil or groundwater due to naturally occurring physical, chemical, or biological processes.
Point of compliance: The point where certain criteria defining the acceptable level of contamina tion for the affected natural environment have to be fulfilled.
Pollutant: A substance that pollutes air, water, or soil, and is the cause of pollution.
Preferential flow: The movement of mobile water and its constituents in preferred pathways through porous media.
Short-, mid-, and long-term: In this work, short-term periods comprise years to decades, mid-term periods comprise decades to centuries, and long-term periods comprise centuries to millennia.
Site surveillance: The monitoring of the landfill site to assure appropriate after-use.
Waste stabilization: A process to reduce the emission potential of the deposited waste to produce an environmentally tolerable residue.
1 Introduction
1.1 Background and motivation
Of all man-made structures landfills are among those with the longest life times in the environment. Landfills were built without containment systems until the 1970s, because the attenuation and buffering capacity of the natural barriers (i.e. geologic conditions) was thought to be sufficient to protect humans and the environment (e.g. Gray et al. 1974; Bagchi 1987). However, as significant groundwater contamination was observed at such landfill sites (e.g. Andersen and Dornbusch 1967; Zanoni 1972; Kerndorff et al. 1980), landfill regulations generally required low-permeability liners at the base of new landfills starting from the 80s-90s (e.g. Austrian landfill directive (MoE 1996b)). In addition to a lining system at the landfill base, a low-permeability cover is typically installed at mod ern landfills after final closure. As a consequence of increasingly stringent regulations with respect to the quality of the deposited waste, the level of waste containment, and landfill operations, the com plexity and cost of landfilling has increased significantly during the last decades (e.g. Environment Agency 2010b). An implication of this trend is the decreasing number of landfills, particularly with respect to MSW landfills in operation, in many industrialized countries (e.g. in the U.S. the number of MSW landfills decreased from 6300 in 1990 to 1750 in 2006 (U.S. EPA 2006); in Germany the num ber of MSW landfills decreased from 560 in 1993 to 330 in 2000 (BMU 2006). As many of these land fills represent a potential source of significant emissions for long time periods (cf. Belevi and Baccini 1989; Krümpelbeck 2000; Kjeldsen et al. 2002), landfill management needs to be prolonged beyond closure to protect humans and the environment. Consequently, as the diversion of waste from landfills to recycling, composting and combustion with energy recovery is increasing and the number of oper ating MSW landfills is on the decline (also due to the increasing size of modern facilities (cf. Krümpelbeck 2000)), the development of long-term management schemes for closed landfills is necessary to prevent adverse effects on humans and the environment.
The management of closed landfills typically includes monitoring (e.g. emissions, groundwater), treatment of emissions (e.g. leachate treatment), and maintenance (e.g. cover, leachate and gas collec tion) of the landfill facilities and is referred to as the aftercare (or post-closure care) period. Aftercare can be ended at a site, when the landfill is not likely to pose a threat to human health and the environ ment (e.g. EC 1999) anymore. As there is a lack of technical criteria to evaluate landfill aftercare and associated environmental risks (Barlaz et al. 2002; Stegmann et al. 2003; Stegmann et al. 2006), it is difficult to develop strategies for the cost-effective protection of human health and the environment at closed landfill sites (Morris and Barlaz 2011). The development of appropriate long-term landfill management strategies is in the interest of both regulatory agencies and landfill owners for several reasons. First, aftercare funding accrual mechanisms currently in place do not typically consider the possibility of aftercare periods exceeding 30 years (minimum period of aftercare for MSW landfills in Europe (cf. EC 1999)). If necessary, reform of the current time-based systems would be most effective if changes were made while landfills are still in active operation and accruing funds. Second, appropriate fiscal management of existing aftercare funds is critical to provide for the proper protection of human health and the environment, the financial well-being of landfill owners, and to prevent the development of landfills without aftercare funding.
1.2 Objectives and scope of the work
The objective of this work is to investigate long-term landfill management with respect to environ mental risks associated with closed landfills. The goal is to develop a methodology to define the state of an environmentally compatible landfill at the end of aftercare. The methodological framework is developed in consideration of typical emission profiles and emission models for different types of landfills, the (long-tem) performance of landfill containment systems, and considerations about the migration of pollutants in the surrounding environment. The application of the method shall provide a basis for the comparison of different aftercare strategies with respect to the duration and intensity of aftercare and the assessment of the environmental risks associated with a specific management strategy.
The following questions are addressed in this work in order to attain the objectives outlined above:
• What is an appropriate method to assess the environmental compatibility of a closed landfill? What would be suitable evaluation criteria?
• How can one investigate and analyse the emission behavior of a landfill? What are relevant pollutants at different landfill types?
• How can landfill stability (in an environmental sense) be defined and evaluated with respect to estimating future emission levels?
• How can technical barriers installed at the landfill and their respective service lives be taken into account?
• How can the potential for natural attenuation processes in the subsurface in terms of envi ronmentally compatible landfill emissions be considered?
• How can substance release from the waste body, barrier performance and reactive transport in the surrounding environment be integrated to determine criteria for terminating landfill after care?
The analysis in this work focuses on environmental aspects of closed landfills. Consequently, despite their potential significance, the economic and social dimensions of long-term landfill management are not addressed in this work.
1.3 Structure of the thesis
In chapter 1 the issue of “long-term landfill management” is briefly highlighted, the objective of the work is described, and the structure of the thesis is outlined (see Figure 1-1). A critical review of approaches for evaluating landfill aftercare including a discussion of their limitations and strengths is provided in the first section of chapter 2. Based on this discussion, a framework for a new evaluation methodology is presented and the procedure to establish the evaluation framework is described in the last section of chapter 2. In Chapter 3 emission characteristics of municipal solid waste (MSW) landfills, municipal solid waste incineration (MSWI) bottom ash landfills, and construction and demolition (C&D) waste landfills are analyzed to evaluate future emission behavior at closed landfills. Studies of the (long-term) performance of technical barriers (i.e. containment systems) are discussed in chapter 4 in the context of estimating future landfill emissions. Chapter 4 also addresses the potentially attenuating effect of natural barriers (i.e. (hydro)geologic conditions at the site) on the spread of
Chapter 3: Landfill emission behavior
Chapter 4:
Technical and natural barriers
Chapter 5:
Methodology to derive landfill completion criteria Chapter 6: Case studies Chapter 1: Introduction Chapter 7: Conclusion & Outlook
Chapter 2:
State of the art & Suggested framework to evaluate landfill aftercare
Figure 1-1: Schematic illustration of thesis structure
contaminants in the environment. Based on the framework introduced in chapter 2, the analysis of landfill emissions, and the effect of barriers on pollutant migration in chapters 3 and 4, a methodology to derive completion criteria for landfill aftercare and to evaluate the environmental risks associated with long-term landfill management is presented in chapter 5. The application of the methodology is illustrated in chapter 6 for two closed MSW landfills and for a closed C&D waste landfill. Finally, the main findings of the work are summarized and conclusions are provided in chapter 7.
The work presented in this thesis is largely based on a research project, which was conducted primarily by the author at the Institute for Water Quality, Resources and Waste Management at the Vienna University of Technology. Reports and articles that have been published as part of this research project or independently by the author may contain some of the text or work included in this thesis. Therefore, the work by Laner (2009), Laner et al. (2009), Laner et al. (2010), Laner et al. (2011a), Laner et al. (2011b), and Laner et al. (2011c) may serve as a source of additional information. Further data on landfill emissions (chapter 3) and for the case studies (chapter 6) can be also obtained directly from the author.
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Postoperationalcareperiod Operationalperiod
Figure 2-1: Different management phases throughout the existence of a MSW landfill
2 Aftercare completion criteria and landfill stability
2.1 Concepts for aftercare and completion
2.1.1 General overview
Apart from a lack of technical criteria and procedures for the evaluation of aftercare and associated environmental risks, different terms and concepts referring to the condition of closed landfills add to the confusion on long-term landfill management. After the operational period of a landfill, different management phases might occur before a final cover is installed (e.g. enhanced emission reduction at the site). In Figure 2-1 it is illustrated that while the post-operational care period starts directly after the end of waste disposal, the aftercare period starts after the landfill has reached its final layout (i.e. cover has been installed). Although the focus of this work is on the aftercare period (=post-closure care period), the management of the landfill during the post operational period is addressed when this is relevant to the approach proposed for aftercare. This would be the case, if measures for enhanced emission reduction after the end of waste deposition are essential for the management concept during landfill aftercare. It would be also the case, if the state of a landfill at the end of aftercare is different from one approach to another (e.g. top cover maintenance as an afteruse activity vs. no more maintenance of the cover). Consequently, aftercare completion may not always mean the same due to different long-term management concepts. Therefore, aftercare completion is defined as the point when the competent authorities accept the end of regulated aftercare, because the closed landfill is not likely to present a threat to human health and the environment (HHE) in the absence of aftercare. In consideration of the underlying management approach this can be a definitive endpoint (i.e. requiring no further care) or the transformation of a closed landfill from post-closure care into a “de minimus care” program (e.g. site surveillance and protection of top cover) (cf. Barlaz et al. 2002). Whereas the former would also imply the end of post-operational care, the latter would leave the landfill in the post-operational care period (cf. Figure 2-1).
Several alternatives have been discussed for the long-term management of landfills. These alternatives include (1) termination of aftercare after a definite time period, (2) perpetual care, (3) complete waste stabilization, (4) specific chemical criteria and (5) a performance based approach (cf. Morris and Barlaz 2011). The first alternative describes a situation in which landfill management by the landfill owner is terminated after specific time period. This period could be 30 years or any other time specified by the regulator. The advantage of this alternative is that it is predictable and the owner
knows what is required for what period of time. However, this alternative leaves society responsible for problems that could arise after the owner is no longer responsible for aftercare at the site. In the termination alternative, the biological, chemical or physical status of a landfill and its potential threat to HHE are not addressed. If termination is at one extreme, perpetual care is considered at the other extreme. In this alternative the owner is required to monitor and maintain the landfill forever. Although this removes uncertainty about the duration of aftercare for owners and authorities and it offers maximum protection of HHE, it is not necessarily cost efficient. If funds are spent to protect against insignificant risks, this is not an optimal use of societal resources (cf. Scharff et al. 2011). In the complete waste stabilization alternative, the landfill is managed until the waste is completely stable with respect to chemical, biological and physical characteristics. At the point of complete stabilization, the waste itself (i.e. without containment) does not pose a threat to HHE. While geotechnical stability may be addressed in terms of post-closure settlement and material properties, chemical stability will be harder to evaluate (e.g. Brunner 1992). Some issues making the evaluation of biochemical stability a difficult task are the accumulation of ammonia in anaerobic leachate of MSW landfills (cf. Kjeldsen et al. 2002), the presence of trace organics and persistent chemicals in the leachate (e.g. Öman and Junestedt 2008; Weber et al. 2011), the heterogeneity of the deposited waste, the heterogeneity of water flow and its effect on waste degradability (cf. Maloszewski et al. 1995; Fellner 2004; Rosqvist et al. 2005), and the challenge of representatively characterizing a landfill (e.g. Chiampo et al. 1996). The fourth alternative is to operate a landfill until specific criteria for the leachate, solids and gas are reached. In the case of leachate from MSW landfills, a BOD5/COD ratio of less than 0.1 has been
suggested as in indicator of stable leachate (Reinhart and Townsend 1997), but it has been recognized to be a necessary but insufficient condition for chemical stability (cf. Barlaz et al. 2002). Criteria for landfill gas might relate to a decrease of gas production rate or a minimum fraction of the expected total gas production has taken place at the site (e.g. Wisconsin Department of Natural Resources 2007). However, typically the lack of consistent (over time) data on landfill gas production and varying collection efficiencies of the gas extraction system will make such evaluation difficult. For waste quality, criteria such as the cellulose plus hemicellulose to lignin (CH/L) ratio have been suggested as indicators for waste stability (e.g. Kelly et al. 2006), again facing challenges of representative sampling and consistent test methods (cf. Knox et al. 2005). A limitation of many of these criteria is that they do not consider site-specific conditions such as local climate, as the requirements for the long-term management of landfills will probably be different in a region with arid climate and in a humid region. The fifth alternative is to adapt post-closure management at the site based on the actual landfill performance. The focus of this alternative is to provide specific guidance on post-closure landfill management to achieve a sequential reduction of the necessary post-closure care intensity. A desired state of the landfill at the end of aftercare is not defined, but aftercare intensity is reduced as warranted by site-specific data ultimately leading to de-minimus care requirements (e.g. activities necessary at any property such as vegetation maintenance) at the site. Based on the general overview of management alternatives for closed landfills given above, the next section analyzes specific approaches which have been suggested for the evaluation and potential com pletion of aftercare at landfills with a focus on MSW landfills. Finally, the major findings from the analysis of long-term management approaches are highlighted, an evaluation framework is developed, and the conceptual foundation of the approach is described in section 2.2.
2.1.2 Review of approaches for landfill aftercare and its completion
Given the range of alternatives for the long-term management of closed landfills, three specific types of approaches to evaluate and manage MSW landfills after closure have been suggested: i) target value approaches define criteria which have to be met to complete aftercare; ii) risk assessment approaches evaluate aftercare in view of the local conditions at the landfill site to quantify risks associated with aftercare activities and aftercare completion; iii) performance based systems for aftercare draw on site specific data, which are used to evaluate the actual level of aftercare and to provide guidance on the progressive reduction of aftercare intensity. A review of specific approaches suggested by different authors (largely) adhering to one of these approaches is presented in this section.
2.1.2.1 Target values to evaluate PCC
In the target value approach, the state of the MSW landfill at which aftercare can be terminated is de fined via generic standards. This approach could address the quality of the deposited waste, the tolerable levels of emissions (landfill gas and leachate), and criteria such as the maximum rate of settlement at the landfill surface. As the specified criteria are generic, they can be applied without further evaluations.
The target values for aftercare completion suggested by Stegmann et al. (2006) are based on approaches to significantly reduce the emission potential of a MSW landfill before the final cover is installed at the landfill. According to investigations by the authors, a MSW landfill will require after care for many decades to several centuries (cf. Heyer 2003; Heyer et al. 2005a), which does not correspond with the goal of aftercare completion within one generation. The reduction of the remain ing emission potential within the waste body is aspired to minimize potential environmental impacts associated with a release of pollutants if containment systems fail at a later time. Controlled infiltration of water into the waste body and the in-situ aeration of the landfill are the main strategies to achieve a low emission potential (cf. Stegmann et al. 2003). In-situ aeration is presented as a promising technology to reduce leachate concentrations, accelerate biochemical degradation processes within the landfill, and complete major settlements within several years (cf. Heyer et al. 2005b).
Stegmann et al. (2006) state that at the end of aftercare the biochemical processes and other conversion processes have to be largely completed and unlikely to be reactivated in the future due to changing conditions at the landfill. The quantitative criteria to terminate aftercare at a site are based on the tech nical (i.e. enhanced emission reduction technologies), the legal (primarily with respect to German reg ulations, cf. BMU (2009)), and the economic (i.e. the costs of different aftercare strategies) conditions concerning landfill aftercare. The suggested target values address tolerable emission levels for landfill gas and leachate (primarily pollutant loads), the quality of the deposited waste (leaching tests and biological degradability), and settlement rates (see Table 2-1). However, Stegmann et al. (2006) emphasize that additional criteria need to be defined on a site-specific basis which relate to engineered landfill elements (e.g. condition of the containment system), the potential of natural attenuation processes taking place in the subsurface below the landfill, and potentially affected vulnerable uses in the vicinity of the landfill. These site-specific criteria are addressed on a conceptual level and tangible criteria or evaluation procedures are not included within the presented approach.
Similar to the above approach, Cossu et al. (2007) proposed a methodology to evaluate the “final storage quality” of a landfill based on a combination of generic criteria and site-specific risk analysis. A landfill is considered to have reached final storage quality when it contains materials of such quality
that no further treatment of emissions into air and water is necessary (Baccini 1989). Starting from a review of different performance parameters, emissions and waste quality, and a comparison of attainable values for defined landfill management technologies, a set of parameters (landfill gas, leachate, and deposited waste) was chosen to evaluate aftercare. Several quantitative criteria are pre sented (see Table 2-1) for a screening evaluation of aftercare at a landfill. If the landfill complies with these criteria, then a site-specific risk analysis (cf. Pivato 2003) is suggested to evaluate environmental compatibility of the emissions at the site.
The evaluation of final storage quality was also proposed by Knox et al. (2005) for 14 year old MSW landfill test cells. The authors state that the organic degradation of MSW is the key process with re spect to achieving final storage quality. The criteria to assess final storage quality are likely to require the removal of 95 to 99.5% of degradable organics, but corresponding biodegradability tests are still rather imprecise and sometimes inconsistent with each other. The target values suggested by Knox et al. (2005) include landfill gas emissions, leachate emissions, and tests to assess the biodegradability of the deposited waste (Table 2-1). The criteria are defined generically based on literature data and regulatory standards. The authors conclude, however, that criteria to assess final storage quality will necessarily be site-specific and that current test methods are not suitable to appropriately characterize final storage quality for a landfill. Thus, operative criteria are still to be developed and should be based on documented cases, where MSW landfills have achieved final storage quality. A case study is pre sented by Valencia et al. (2009), who evaluate waste from a pilot scale bioreactor test cell by applying the waste acceptance criteria for inert waste landfills (EC 2003). They reported that the quality of the waste did not comply with waste acceptance criteria values after two years of operation (note that this would not be expected anyhow). However, as the waste acceptance criteria were not designed as target values for aftercare completion at MSW landfills, as for example ammonium is ignored as a leachate quality parameter, these criteria are not included in the discussion on target value approaches.
Krümpelbeck (2000) proposed another approach to evaluate the state of the landfill at which aftercare might be completed using generic values. Based on an evaluation of emission data from German MSW landfills, Krümpelbeck (2000) identifies leachate emissions as the primary long-term threat at MSW landfills. Consequently, the suggested target values refer to the load of chemical oxygen demand and ammonia-nitrogen in the leachate (see Table 2-1). Although the loads are suggested as the primary indicators, critical concentration levels are also presented for these parameters. These criteria are based on the assumption that 9% of the original emission potential of the deposited MSW, calculated via trend extrapolations of leachate data, will be released from the landfill over 500 years. In addition to these criteria, other values are discussed as leachate-based completion criteria, such as water quality standards for the inflow of drinking water purification plants, and it is emphasized that the application of the presented criteria is only suitable if the landfill base is located at least several meters above the groundwater and emissions are compatible with the planned future use of the site. Krümpelbeck (2000) concludes that the target values enable an initial assessment that must be complemented by site-specific criteria to determine when completion of aftercare is possible. Hence, the approach provides screening level indicators for leachate, but does not represent an operative procedure to evaluate aftercare.
In general, all of the authors of target value approaches emphasize that additional site-specific evalua tions are needed to complement the suggested values before a decision on aftercare completion can be made. Although no specific procedure is suggested, the authors agree that a site-specific assessment
needs to address the risk of environmental pollution at the site, especially with respect to groundwater. Most of the approaches include criteria for the quality of the deposited waste with a focus on its biodegradability. However, the issue of a representative characterization of the landfill body (cf. Chiampo et al. 1996; Sormunen et al. 2008) and the consistency of different test methods (e.g. Laner et al. 2011a) has not yet been handled on an operative level. In the approaches described by Stegmann et al. (2006) and Cossu et al. (2007), the target values are derived in consideration of achievable landfill properties (based on enhanced emission reduction measures) and they may not necessarily be associated with environmentally compatible emissions. The latter is discussed by Ehrig (2002) who points out the danger of specifying target values based on achievable rather than on environmentally protective levels.
Apart from the approach suggested by Stegmann et al. (2006), the approaches presented in Table 2-1are conceptual and not specific with respect to the underlying definition of the state at which a landfill might be released from aftercare. Although, Knox et al. (2005), Cossu et al. (2007), and Valencia et al. (2009) use “final storage quality” to describe this desired state, it has been previously concluded that this is not yet an operative definition and that it probably cannot be defined in a generic way (e.g. Baccini 1989; Brunner 1992; Hjelmar and Nedenskov 2007). In conclusion, the presented target value approaches range from specific guidance on aftercare (cf. Stegmann et al. 2006) to screening level assessments (e.g. Knox et al. 2005). All authors acknowledge that aftercare completion at MSW landfills is a site-specific exercise and thus supplementary evaluations to generic target values are necessary to evaluate completion.
Stegmann et al. (2006) Cossu et al. (2007) Knox et al. (2005) Krümpelbeck (2000)
Leachate COD: 5 – 20 g/m²*yr,
NH4-N: 2.5 – 10 g/m²*yr, Cl: 10 – 20 g/m²*yr, AOX: 0.01 – 0.05 g/m²*yr (Emissions to subsurface) COD: < 200 mg/l
BOD5/COD ratio & NH4-N
concentrations: mentioned as indi
cators, but no value provided.
NH4-N: ≤10 mg/l Concentrations & loads:
COD: ≤16 – 70 mg/l, NH4-N: ≤9 – 20 mg/l COD: ≤3 - 14 g/m²*yr, NH4-N: ≤1.8 – 4 g/m²*yr
Landfill gas Methane production rate: < 25 m³
CH4/h and <0.5 liters CH4/m²*h
Hydrocarbon emissions (flame zation detector measurements): < 25 ppm
Landfill gas generation rate: < 25
m³/h
Area-specific methane generation
rate: < 1 liter CH4/m²*h
(CO2+CH4)/N2 ratio: no value given
Landfill gas emission rate: ≤ 8.4
-liters/m²*h
Trace gas concentrations: ≤ 0.5 H2S
ppbv
Waste quality Eluate (L/S=10 l/kg):
TOC: ≤150 mg/l,
NH4-N ≤50 mg/l,
cyanide ≤0.1 mg/l,
AOX ≤0.5 mg/l (additionally: heavy
metals, organic compounds, pH, EC) Biodegradability:
Respiratory index (RI4): ≤ 2.5 mg
O2/g dry matter (DM)
Methane generation potential in 21
days: 10 liter/kg DM
Biodegradability:
Respiratory index (RI4): ≤ 2.5 mg
O2/g DM
Methane generation potential in 21
days: 10 liter/kg DM
Biodegradability:
Loss on Ignition (corrected for plas
tics): ≤25 %
Acid detergent fiber (corrected for
plastics): ≤2.5 %
Cellulose/lignin ratio (corrected for
plastics): < 0.2
Biochemical methane potential
(BMP): ≤0.2 m³ CH 4/Mg DM
Landfill settlement Site-specific assessment (90
overall settlement completed)
% of - -
-Comments Site-specific criteria addressing
geotechnical stability, landfill ele
ments (e.g. base lining system), and
hydrogeology to be set.
All target values are
screening purposes whether a subsequent should be implemented. intended for to decide risk analysis
Biodegradability tests are not precise
and site-specific assessment is
required in addition.
Concentration levels are applicable
only if leachate generation rate is
below 200 mm/yr.
Table 2-1: Completion criteria suggested within different target value approaches
2.1.2.2 Environmental risk assessment to evaluate PCC
As long as a landfill represents a hazard and there is a good which can be damaged (e.g. human health or environmental compartments), some level of risk is associated with the landfill. Risk assessment has been applied to landfills, often with a focus on leachate emission levels and groundwater pollution (e.g. Butt and Oduyemi 2003). With respect to landfill aftercare, an accept able level of risk has to be defined for the state of the landfill at the end of aftercare (cf. Pivato 2003). Hence, to evaluate the risk of a closed landfill, potential negative effects on HHE and the probability of their occurrence need to be assessed. Specific approaches which adhere to the con cept of landfill risk assessment for evaluating aftercare are described below and summarized in Table 2-2.
Scharff et al. (2007) state that a robust risk assessment is needed to end aftercare at landfills. Within a pilot study on the landfilling of primarily inorganic waste, Scharff et al. (2011) developed an approach for determining aftercare completion criteria as a part of an integrated procedure to evaluate aftercare. Though recognizing the importance of additional evaluation criteria such as landfill gas parameters (for landfills containing biodegradable waste) or parameters associated with functional stability1, the work presented by Scharff et al. (2011) focuses on leachate risk
assessment. The long-term impact of leachate emissions is evaluated based on geochemical modeling and the subsequent comparison of maximum concentration levels to water quality criteria. The procedure is comparable to the source-pathway-receptor approach, which was applied to determine the waste acceptance criteria within the EU landfill directive (cf. Hjelmar et al. 2001; Hjelmar et al. 2005). The major difference is that the suggested approach employs a more sophisticated reactive transport model to describe contaminant migration through the soil towards the point of compliance. The modeling scenario presented in Scharff et al. (2011) is based on a largely inorganic waste landfill with an average waste thickness of 20 meters, a net water in filtration rate of 300 mm/yr, and an assumption that the liner system at the landfill base failed com pletely. The application of the approach revealed chloride and sulfate as the contaminants potentially not complying with the quality standards at the point of compliance (PoC - a hypothetical drinking water well in the groundwater downstream of the landfill). It should be emphasized that these results relate to leachate from largely inorganic landfills. For landfills containing biodegradable waste, they suggest that after the organic matter has been degraded, the behavior of the landfill body may converge towards the behavior of a largely inorganic landfill (cf. Mathlener et al. 2006). Parameters typically important in the leachate from MSW landfills (e.g. NH4-N, COD) have not been addressed. Scharff et al. (2011) conclude that a robust risk assessment
approach is needed to determine aftercare completion criteria in view of the conditions at the site and that the evaluation of aftercare completion cannot be based solely on absolute numbers.
Another risk assessment approach primarily based on modeling of landfill leachate release and forward modeling of contaminant transport processes in the subsurface has been presented by Hall et al. (2006; 2007a). The modeling is carried out with LandSim2.5 (Environment Agency 2004),
1 defined in Morris and Barlaz (2011) as a landfill that is no longer a threat to HHE based on its performance
which is used to predict the time period until “equilibrium status” with the environment can be reached at the landfill site, based on specific assumptions with respect to long-term liner and cap performance. Equilibrium is defined as the state when emissions from a landfill occur at a rate that allows sufficient natural attenuation in the surrounding environment to prevent environmental harm, so management is no longer required (Hall et al. 2007a). Consequently, if equilibrium condi tions are reached at a site, landfill aftercare can be terminated (Hall et al. 2007b). Within the pre sented study, the risk assessment methodology has been primarily applied to demonstrate the effect of waste diversion and pretreatment options (e.g. MBT residues, incineration) in the UK on the time period until environmental equilibrium can be achieved. The authors state that aftercare completion can only be achieved if a landfill has stabilized physically, chemically, and biologically to a degree that the undisturbed contents are unlikely to pose a pollution risk at the site, which implies that the presented modeling approach needs to be complemented with other criteria to form a framework to address aftercare completion. However, this framework has not yet been proposed. In contrast to the approaches described above, the methodology suggested by Boerboom et al. (2003) does not assess the pollution risk emanating from a closed landfill but rather the costs of environmental risks associated with aftercare. The methodology is designed to estimate appropriate funding for aftercare activities, which should be based on the potential financial risks present at a site. The risk assessment builds on expert estimates of failure probabilities for specific events (e.g. unsatisfactory inspection of the landfill cover) that are linked to the occurrence of unwanted events in a fault tree analysis. The investigated unwanted events do not comprise exceptional risks (e.g. earthquake) and relate to a large and uncontrolled contamination of groundwater, damage to the final cover, or an early need for replacement of the final cover. The probability of occurrence for an unwanted event is calculated via Monte Carlo analysis and the sum of costs to undo the unwanted events for a defined period is calculated as the financial risk during aftercare. Although the metho dology is not intended to specify a procedure for landfill completion (risks are calculated for specific aftercare durations), it may represent a valuable tool to provide appropriate funding for aftercare activities, especially if it is widely applied and the model is parameterized from a growing database.
Out of the risk assessment approaches summarized in Table 2-2, only the approach suggested by Boerboom et al. (2003) directly addresses MSW landfills, however, only in terms of financial risks during aftercare. The other approaches were developed to assess (primarily) the risk of ground water pollution for largely inorganic landfills (Scharff et al. 2011) or for virtual landfills to analyze different waste pretreatment options before landfilling (Hall et al. 2007), respectively. Although these approaches might prove valuable for an assessment of environmental risks associated with closed MSW landfills, they have not yet been integrated to form an evaluation framework for after care. There is a high level of uncertainty involved in a risk assessment and the transparency of modeling assumptions is significant for an understanding of the outcome. Hence, there is a need for consistent procedures that allow for an objective evaluation of the environmental risk at a closed landfill. This is highlighted by the work of Hall et al. (2006; 2007a), who point out the complexity in their modeling due to assumptions on containment system performance and subsequent effects on the interrelationships between leachate quality, release rates and concentrations at the PoC in the groundwater. Consequently, sensitivity analysis and the handling of inherent uncertainties are
Authors Modeling approach Application Comments
Scharff et al. Long-term modeling of conta- Case study on a largely inor- Suggested as a part of the
(2011) minant migration to a point of ganic landfill (Cl and SO4 iden toolbox to assess aftercare
compliance and comparison to tified as critical leachate para completion
specific standards meters)
Hall et al. (2007) Long-term modeling of conta- Hypothetical landfills with dif- A procedure for aftercare
minant migration to a point of ferent waste qualities sited in a completion incorporating compliance and comparison to specific model environment the modeling results has not
specific standard (leachate parameters at equili been suggested.
brium level are presented)
Boerboom et al. Probabilistic risk assessment to Used as a cost calculation me- No guidance on aftercare or
(2003) estimate potential costs asso thod for aftercare in several completion, but could be a
ciated with environmental risks provinces of The Netherlands basis to accrue appropriate
during aftercare aftercare funding
essential for the comprehensiveness of the modeling results. In conclusion, while the presented risk assessment approaches could be a substantial part of an aftercare evaluation procedure, they are expensive and uncertain. As such, the utility of risk assessments in the development of aftercare completion remains to be determined.
Table 2-2: Methodological basis and application of risk assessment suggested to evaluate PCC
2.1.2.3 Performance-based system for PCC
As a consequence of potentially long aftercare periods for MSW landfills, performance-based eval uations have been suggested for long-term management of closed MSW landfills (Barlaz et al. 2002). In general, such approaches are based on landfill monitoring and performance data, which are used to evaluate the actual state of the landfill and to determine appropriate aftercare activities. Hence, the evaluation procedures are site-specific and provide guidance on the sequential reduction of aftercare intensity that may, if warranted by performance data, ultimately lead to aftercare com pletion. Different approaches adhering to this concept are described in this section and summarized in Table 2-3.
A performance-based system for evaluating aftercare requirements at MSW landfills referred to as the evaluation of post-closure care (EPCC) methodology has been presented by Morris and Barlaz (2011). The EPCC methodology addresses the four primary aspects of landfill aftercare monitoring and maintenance (i.e. leachate quality and quantity, gas management, groundwater monitoring and protection, and cover maintenance) in a user-friendly modular system. It provides long-term stewardship of landfills by assessing their current and future impacts to the environment based on the evaluation of “functional stability”. Functional stability is used to define a closed landfill that does not present an unacceptable threat to HHE in the absence of aftercare, but with some remain ing level of control to protect the cover (Solid Waste Association of North America Bioreactor Committee (2004) cited in GeoSyntec (2006)). The methodology establishes a site-specific basis for decisions on maintaining, extending, reducing, or modifying aftercare activities while being protective of the environment. Logic diagrams are used for each aspect of aftercare (i.e. for each
module) and the modules can be sequentially evaluated (prerequisites module, leachate module, gas module, groundwater module, and cover module). The aspired end-use and final condition of the landfill are defined from the outset of the evaluation. Conservative assumptions are used within the evaluation procedure and proposals to modify an aftercare activity are driven by data. The application of the methodology generally involves analyzing statistical trends in leachate, landfill gas generation, and groundwater quality, as well as additional biological, chemical, and physical data, to demonstrate that gas production is stable or decreasing and leachate quality is constant or improving. Once a change in aftercare is implemented, the owner is expected to verify no adverse effect by “confirmation” monitoring followed by surveillance monitoring at a decreasing frequency. Monitoring procedures also identify high and low level “trigger” conditions requiring immediate responsive action to be taken to resolve the condition. The system allows for multiple outcomes in which the requirements for each aspect of aftercare may vary significantly. Three possible levels of analysis are built into the methodology: a) in a source evaluation the compliance with target values may be demonstrated at the source (e.g. leachate quality < drinking water standards); b) in a point of compliance evaluation, it is demonstrated that the landfill does not pose an unacceptable threat at the PoC; and c) in a point of exposure (PoE) evaluation it is demonstrated that the landfill does not pose an unacceptable threat at the PoE (Morris and Barlaz 2011). The potential for a harmful release to the environment is analyzed before any aspect of aftercare may be reduced or discontinued. Thus, the EPCC methodology determines a level of aftercare which is consistent with the actual state of the landfill and the sensitivity of the surrounding environment. This is the basis for progressively reducing aftercare and finally turning the landfill into a custodial care program (i.e. aftercare completion). The custodial care program represents a level and type of activities which would be required at other sites and thus would not be specific for MSW landfills (cf. Pivato and Morris 2005; ITRC 2006).
Application of some components of the EPCC methodology to evaluate appropriate aftercare at a specific MSW landfill in Florida has been described by Sizirici (2009). A set of relevant parameters (e.g. leachate: ammonia-nitrogen, chloride, iron, VOCs or landfill gas: remaining gas generation potential) was identified and estimates of future emission levels were derived for the case study landfill (cf. Sizirici and Tansel 2010). Based on a risk assessment at the site, Sizirici (2009) concluded that landfill gas management is no longer necessary, whereas monitoring of leachate and groundwater has to be continued. Surveillance of cap integrity also remains an integral part of aftercare activities at the landfill. Hence, the aftercare period at the site can be reduced for some landfill elements (e.g. gas collection) but is required for others (e.g. leachate management) to be protective of HHE.
Recently, Sizirici et al. (2011) presented a screening procedure for a preliminary assessment of aftercare needs at closed landfills. The procedure is based on expert evaluations (scale from 1 to 10) of site-specific parameters (e.g. climate, operational factors, leachate management, gas management, etc.), which are combined using a ranking algorithm (i.e. by assigning weights to different factors). The overall score from the algorithm is used to categorize the landfill conditions as critical, acceptable, or good. “Critical condition” at a site indicates that the landfill may represent a threat to HHE and thus, aftercare activities need to be adjusted. “Acceptable condition” as a result of the evaluation confirms current aftercare intensity and “good condition” as an outcome of the
evaluation indicates the potential for a reduction of aftercare activities. However, the suggested aftercare evaluation procedure does not provide specific guidance on the intensity of aftercare or the completion of aftercare activities.
A performance-based approach for aftercare based on the potential of naturally occurring or en hanced natural attenuation (NA) processes (e.g. via waste aeration) at a landfill has been described by van Vossen (2010). This approach aims at lasting emission reduction at closed MSW landfills and is based on the full scale demonstration of the methodology at three case study landfills in The Netherlands (cf. van Vossen et al. 2007; van Vossen et al. 2009a; van Vossen et al. 2009b). The model to demonstrate the capability of natural attenuation processes to phase out unacceptable levels of contaminants is referred to as the SANA (Sustainable Aftercare of landfills based upon Natural Attenuation) model (van Vossen 2010). As one of the demonstration landfills has been partly built without a base lining system, the SANA model has the capability to analyze the poten tial for natural attenuation in the landfill body as well as in the pollution plume below the landfill and in the groundwater. The conditions in the landfill are characterized and the model evaluates the state of biochemical, geochemical, and hydrological processes in consideration of performance indicators (e.g. in-situ temperature, settlements, BOD5/COD ratio, ammonia-nitrogen, gas
production rate, and CH4/CO2 ratio) that are used to describe the extent of organic matter
stabilization. The goal of enhanced emission reduction activities within the SANA model is to replace the need for an impermeable final cover by a low emission potential of the waste, which is expected to result in landfill emissions meeting acceptable levels and consequently allowing for aftercare completion. If acceptable leachate emission levels cannot be achieved at a site, an environmental risk assessment is suggested to determine the necessity of mitigation measures for preventing inacceptable groundwater pollution. In essence, the suggested approach promotes a specific aftercare strategy (i.e. enhanced emission reduction based on NA processes) and describes its application to demonstration landfills, but does not yet constitute a consistent methodology to evaluate aftercare and aftercare completion. Van Vossen (2010), states that such a methodology will be based on the final results of the demonstration projects and is currently under development. The performance-based evaluations of aftercare shown Table 2-3 are essentially site-specific, allowing for long-term landfill management to be adapted to local conditions. Among the presented approaches, the EPCC methodology represents the most tangible evaluation procedure, providing operative assessment protocols to decide on an appropriate level of aftercare. Whereas the EPCC methodology establishes a consistent aftercare evaluation framework, the approach suggested by van Vossen (2010) follows a bottom-up strategy of demonstrating the performance of natural attenuation processes to reduce emissions at full scale landfills and developing a consistent evalua tion methodology based on the outcome of current demonstration projects. However, within the evaluation methodology an environmental risk assessment and potential site remediation may be necessary if admissible emission levels could not be met with the emission reduction approach. In addition, for those landfills not equipped with a bottom liner no operative protocol to monitor NA at MSW landfills has been suggested yet and regulators may not accept the local groundwater as a long-term treatment filter for waste management processes (cf. Christensen et al. 2000).
Authors Methodology Application Comments
EPCC methodol ogy
(Morris and Barlaz 2011)
Modular approach for the eval
uation of environmental impacts associated with aftercare addressing data collection, lea chate management, gas man agement, groundwater moni toring, and cover performance.
Evaluation is used as a basis to progressively reduce aftercare,
ultimately leading to completion while being protective of the environment. Application was
demonstrated at a hypothetical case study site.
Operative methodology providing specific protocols for long-term landfill man agement.
Sizirici et al.
(2011)
Ranking algorithm based on ex
pert evaluations of site-specific
factors resulting in a pre liminary assessment of appro
priate aftercare at a site.
Factor-specific ordinal scores
based on site performance as
signed by experts and then
weighted to derive an overall landfill score. Application at two sites was presented.
Tool is dependent on expert judgment and qualitative analysis.
SANA model
(van Vossen (2010))
Demonstration of natural
uation as a feasible approach for
aftercare to minimize long-term
environmental risks at MSW
landfills based on performance data.
A natural attenuation (or bio
reactor) approach is promoted to
achieve a lasting reduction of the emission potential at three full-scale demonstration landfills.
Bottom-up approach to
vide guidance on aftercare. Consistent methodology is
to be developed based on the case study results.
Table 2-3: Methodological basis and application of performance-based systems to evaluate PCC
Another fundamental difference between the concept suggested by van Vossen (2010) and the EPCC methodology is that the former embraces a strategy to enhance emission reduction to de crease emissions to low levels without a long-term low-permeability cover, whereas the latter does not require a strategy to decrease the emission potential of the waste body, as the focus lies on actual emission levels and emission trends at the landfill. Where no steps are taken to decrease the emission potential of the waste body, maintenance of a low-permeability top cover is expected to be part of the custodial care program within the EPCC methodology. Indeed, regardless of the long-term management approach at a landfill, some level of cover maintenance and associated site care activities will always be required using the EPCC methodology.
The approach presented by Sizirici et al. (2011) does not rely on measured landfill performance data like the other approaches listed in Table 2-3, but on expert evaluations of different factors ad-dressing aftercare at the landfill. The procedure also does not give guidance on specific aftercare activities or completion criteria. In general, the application at case study sites is of paramount importance for all performance-based approaches, as this will be necessary to assess their practicability with respect to aftercare duration and completion.
2.1.3 Discussion of approaches to evaluate aftercare
The aim of any evaluation of landfill aftercare and completion is to address the risks associated with a closed landfill in a consistent and transparent manner and thereby allow decision makers to comprehend underlying assumptions as well as associated residual risks. Table 2-4 summarizes the major characteristics of the target value, risk, and performance-based approaches. As described in
Characteristic Target value
approaches*
Risk assessment approaches
Performance-based approaches
Site specific No Yes Yes
Data collection in addition to ▪ Waste sampling and ▪ Waste sampling and ▪More extensive moni
standard emission monitoring analysis (i.e. leaching analysis (potentially) toring
and biodegradability ▪More extensive moni
tests) toring (potentially)
Outcome verification ▪Not necessary ▪Not included
